The invention relates to a display, in particular an autostereoscopic or holographic display, for representing preferably three-dimensional information, wherein the stereo views or the reconstructions of the holographically encoded objects can be tracked to the movements of the associated eyes of one or more observers.
Displays for displaying three-dimensional information are known in a multiplicity of embodiments. Besides embodiments which require additional aids such as shutter or polarization spectacles for viewing the spatial scene, autostereoscopic displays do not require such aids. Without additional measures, however, in the latter displays the 3-D scene can be viewed only in a narrow spatial region, the so-called observer region. In order that the 3-D scene can also be seen conveniently in a large horizontal angular range, devices have been developed which allow said observer region to be tracked to the eyes of the observer. Such a system has been described e.g. by the applicant in the patent specification DE 103 39 076 B4. The applicant has likewise described a series of holographic display devices, e.g. in EP 1 563 346 B1 or EP 1 792 234 B1, wherein a 3-D scene can be perceived in a narrowly delimited observer region as a spatial reconstruction of the intensity distribution by means of holographic diffraction patterns being encoded in a spatial light modulator. Here as well it is expedient for the observer region to be tracked to the eye movements of one or more observers. For this purpose, such devices have a recognition system that determines the positions of the eyes of the observers and forwards the data to a system controller. The recognition systems often operate in a camera-based manner, wherein the eye positions are determined by means of image processing algorithms. In accordance with the respective eye positions, the system controller controls mechanical or electronic light deflection means such that the center of the observer region assigned to the respective eye position as far as possible corresponds to the respective eye position to the greatest possible extent. If desired or necessary, at the same time the image content or the reconstruction of the 3-D scene can be adapted to the new eye position.
In such a display, an illumination unit generates light that is collimated to the greatest possible extent with the required wavelength spectrum with which the spatial light modulator into which the stereoscopic views are written or the holographic information is encoded is illuminated. In the case of holographic displays, the light must additionally be capable of interference at least in a region required for encoding a pixel of the 3-D scene, i.e. said light must be sufficiently coherent. The light deflection means can be situated upstream and/or downstream of the spatial light modulator.
The illumination unit can also be configured in a controllable manner such that it can direct light in predefinable spatial directions. For this purpose, for example, displaceable illumination columns can be situated in direct proximity to the focal plane upstream of a cylindrical lens array. The illumination columns can be controllably selected for example from an active light source matrix, which can be embodied e.g. as an OLED matrix. It is also possible to use a planar light source, in front of which is arranged an array of slit diaphragms that are variable in a drivable manner in terms of their horizontal position. Such a diaphragm array can be configured as an LCD matrix, for example. In this case, each column forms a secondary light source which illuminates that cylindrical lens of the cylindrical lens array which is assigned to it. The horizontal position of the illumination columns with respect to the center line of the assigned cylindrical lens determines the horizontal angle—emitted by the respective cylindrical lens—of the partial beam that is collimated to the greatest possible extent. In this case, a plurality of illumination columns can also be activated simultaneously in order to increase the emitted angular range and thus the size of the assigned observer region. Furthermore, the horizontal deviation of the position of the illumination columns with respect to the center line of the assigned cylindrical lens can vary over the area of the cylindrical lens array in order e.g. to realize an additional field lens function and thus to adapt the horizontal diameter of the assigned observer region to the observer distance. The cylindrical lens array can have a diaphragm array that avoids crosstalk between the illumination columns assigned to a cylindrical lens and neighboring cylindrical lenses. Undesired secondary observer regions can thus be avoided.
The number of illumination columns assigned to a cylindrical lens determines the number of possible horizontal deflection angles. This number cannot be increased arbitrarily, since the primary and/or secondary light sources have technically dictated minimum dimensions. Moreover, the required luminance increases, the smaller the dimensions become. For a large horizontal movement region in which a plurality of observers can also be situated, however, a large number of finely gradated light deflection angles are required for observer tracking. Therefore, a series of additional measures have already been proposed for increasing said movement region and thus the number of possible deflection angles. By way of example, in the American Patent Specification U.S. Pat. No. 7,791,813 B2, arrays of electrically controllable electrowetting cells were to be used for beam deflection. However, such arrays are complicated to produce and have a restricted aperture on account of the cell height. Mechanical deflection means such as deflection mirrors or rotatable prisms, which were likewise proposed, are sluggish and require a large structural volume.